Cases2 cases

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1. IL-0386 After a move to Google Cloud, Postgres connection timeouts and memcached i/o timeouts spiked on GKE nodes

   incident.io2023

   Symptoms

   Shortly after incident.io moved its infrastructure fully into Google Cloud, the application saw a larger-than-normal number of Postgres connection timeouts, and new database connections per second were in the hundreds, spiking up and down. At the same time, the memcached instance used for transient data and faster API responses had sporadic connection timeouts.

   Intermittent timeoutsPacket loss

   Trigger

   After the move to Google Cloud, the application opened hundreds of new Postgres connections per second, and an accidental database join made it send thousands of duplicate calls to an external third party in parallel.

   Root cause

   Capacity exhaustion

   Component

   CNI pluginDatabaseIn-memory cache

   Contributing factor

   Unreviewed defaultsOverlapping failures

   Detection

   An incident was declared when the number of Postgres connection timeouts rose above normal. The remaining cache timeouts were traced through the logs of the Kubernetes node that served an affected request, the request's trace and the node's metrics.

   Remediation

   • Doubled the maximum Postgres connection lifespan from 15m to 30m
   • Made the Postgres connection pools static so they always keep N connections open
   • Raised the memcache client's MaxIdleConns from 2 to 20
   • Moved temporarily from Google's hosted memcached to a memcached inside the Kubernetes cluster
   • Shipped the fix for the accidental database join that made thousands of duplicate external calls

   Action items

   • Set more sensible concurrency limits for outbound network calls

   Lessons

   Network timeouts are not always local to one request or pod: when they appear, the whole activity of the node, including other pods on it, needs to be checked. Staying within a provider's rate limits does not keep outbound calls from affecting a node, so outbound network calls need more sensible concurrency limits.

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2. IL-0472 Node-to-pod traffic and DNS failed on Tinder's 605-node Flannel cluster when every node's ARP cache passed gc_thresh3

   Tinder2019

   Symptoms

   In the early morning of 8 January 2019 Tinder's platform had a persistent outage. Communication from nodes to pods failed, and so did DNS lookups, because DNS ran inside the Kubernetes cluster.

   Service outageNetwork unreachableDNS resolution failures

   Trigger

   Earlier that morning, pod and node counts on the cluster were scaled up in response to an unrelated increase in platform latency.

   Root cause

   Capacity exhaustion

   Component

   Linux kernelCNI plugin

   Contributing factor

   Unreviewed defaults

   Remediation

   • Raised gc_thresh1, gc_thresh2 and gc_thresh3 on the nodes
   • Restarted Flannel so it re-registered the missing networks

   Lessons

   Tinder lists the outage among its learnings about network fabric limits: with Flannel over VXLAN, every node, and every pair of nodes that exchange pod traffic, adds entries to each node's ARP table, so at 605 nodes the default gc_thresh3 hard cap was exceeded on all nodes.

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